The present invention relates to means for enhancing the radar return of a body such as an aerospace vehicle, and more particularly, to means providing a desired fraction of cross-polarization in the return.
The scattered electromagnetic field from a body with edges, such as an aircraft, contains polarization components that are not present in the incident field. This is commonly referred to as cross-polarization. Small target drone aircraft or similar bodies used for electronic countermeasure purposes often include reflective augmenters to enlarge the size of a radar return signal from it to simulate a larger craft. The resulting radar return signal has virtually no cross-polarization in it, however, and thus does not realistically simulate the desired aircraft or other object. A level of -10 db below the self-polarization has been commonly taken as a reasonable estimate of the actual cross-polarization in the radar cross section of typical (unaugmented) aircraft.
It is an object of the present invention to provide a retro-directive lens system having a radar cross section that reflects back a cross-polarized component having a desired magnitude compared to the self-polarized component to provide the best possible simulation of a given object or body.
At the same time, another object is to provide such a cross-polarizing reflector having no loss or degradation in the extent of directional response from that of a conventional Luneberg lens reflector.
One known type of reflector producing cross-polarization consists of a Luneberg lens, the entire surface of which is covered with a 45.degree. wire grid structure and is known in the art as a bird cage Luneberg reflector. As is known by those skilled in the art, this reflector produces nearly equal self and cross-polarization in the reflected signal from an incident wave of vertical polarization. This would not be suitable to solve the present problem.
Another cross-polarization device is a dihedral corner reflector arranged with its V -intersection line in a vertical plane and inclined 45.degree. to the left or right of an incident horizontally or vertically polarized wave. But this structure produces a complete conversion of self-polarization into cross-polarization, and is therefore not suitable for the present purpose.